The proposed research project is concerned with the properties and functions of membrane-bound ribosomes in the chloroplast of Chlamydomonas reinhardtii and in two bacteria, Rhodospirillum rubrum and Bacillus amyloliquefaciens. The project consists of four parts. (1) A model for the assembly of polysome-membrane complex in the chloroplast will be established. This model suggests that the attachment of ribosomes to the membranes depends on the translation of the m-RNA. Antibiotics will be used to show that this attachment depends on peptide chain initiation. Labeling experiments will also be done to ascertain whether there are two separate pools of chloroplast ribosomes. (2) The occurrence of membrane-bound ribosomes will also be examined in the bacteria R. rubrum and B. amyloliquefaciens, by correlated biochemical and electron microscopic experiments similar to those carried out in C. reinhardtii. Specifically, the role of the nascent chain and the involvement of ionic bonds in the ribosome-membrane interaction will be explored. (3) The role of the membrane-bound ribosomes in the synthesis of membrane proteins will be examined in the chloroplast of C. reinhardtii and in R. rubrum. Bound polysomes isolated from both systems will be translated in vitro and the products will be characterized by gel electrophoresis and compared to the labeled protein profiles of the corresponding membranes. (4) The role of the presumptive membrane-bound ribosomes in B. amyloliquefaciens in the synthesis of secreted enzymes will be examined. BIBLIOGRAPHIC REFERENCES: Iwanij, V., Chua, N.-H. and Siekevitz, P. (1975) The synthesis and turnover of ribulose bisphosphate carboxylase and of its subunits during the cell cycle of chlamydomonas reinhardtii. J. Cell Biol. 64, 572-585. Chua, N. -H. and Bennoun, P. (1975) Thylakoid membrane polypeptides of Chlamydomonas reinhardtii: Wild-type and mutant strains deficient in photosystem II reaction center. Proc. Nat. Acad. Sci, USA 72, 2175-2179.